Delay line for travelling-wave tubes

ABSTRACT

A delay line for travelling-wave tubes is formed by a hollow wave guide having hollow cylindrical metallic cylinders individually disposed concentrically of and spaced-apart along the longitudinal axis of the travelling-wave tube and intermediate electrodes disposed between adjacent metallic cylinders. Each of the metallic cylinders is connected to the inner wall of the wave guide on opposite sides of the wave guide from adjacent metallic cylinders. Each of the intermediate electrodes are in the form of a metallic ring which bears against the inner wall of the hollow wave guide and which includes a central inner aperture having a diameter which is substantially larger than the outer diameter of the metallic cylinders. The provision of the intermediate electrodes extends the upper and lower limiting frequencies whereby the dispersion curve of the travelling-wave tube becomes steeper and the pass band is reduced to prevent pre-oscillation and parasitic operation.

United States Patent 1 1 Veith et a1. 1 1 June 12, 1973 [54] DELAY LINE FOR TRAVELLING-WAVE 3,102,969 9/1969 Arnaud 315 393 3,234,426 2 1966 Hell 315 36 TUBES [73] Assignee: Siemens Aktiengesellschaft, Berlin and Munich, Germany [22] Filed: May 7, 1971 [21] Appl. No.: 141,371

Related US. Application Data [63] Continuation of Ser. No. 848,162, Aug. 7, 1969,

abandoned.

[30] Foreign Application Priority Data Sept, 12, 1968 Switzerland 13667/68 [52] US. Cl 333/31 A, 315/36, 315/393 [51] Int. Cl HOlj 25/34, H03h 7/30 [58] Field of Search 333/31; 315/36,

[56] References Cited UNITED STATES PATENTS 3,102,969 9/1963 Arnaud 315/393 3,181,024 4/1965 Sensiper 315/35 3,234,426 2/1966 Heil 315/393 3,353,121 11/1967 Dube 333/31 Inventors: Werner Veith, Franz Gross, Konrad Pobl, all of Munich, Germany Primary Examiner-Rudolph V. Rolinec Assistant Examiner-Marvin Nussbaum Attorney-Hill, Sherman, Meroni, Gross & Simpson [57] ABSTRACT A delay line for travelling-wave tubes is formed by a hollow wave guide having hollow cylindrical metallic cylinders individually disposed concentrically of and spaced-apart along the longitudinal axis of the travelling-wave tube and intermediate electrodes disposed between adjacent metallic cylinders. Each of the metallic cylinders is connected to the inner wall of the wave guide on opposite sides of the wave guide from adjacent metallic cylinders. Each of the intermediate electrodes are in the form of a metallic ring which bears against the inner wall of the hollow wave guide and which includes a central inner aperture having a diame ter which is substantially larger than the outer diameter of the metallic cylinders. The provision of the intermediate electrodes extends the upper and lower limiting frequencies whereby the dispersion curve of the travelling-wave tube becomes steeper and the pass band is reduced to prevent pre-oscillation and parasitic operation.

3 Claims, 4 Drawing Figures DELAY LINE FOR TRAVELLING-WAVE TUBES This is a continuation of application Ser. No. 848,162, filed Aug. 7, 1969, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a delay line for travellingwave tubes, and more particularly to travelling-wave amplification tubes of high capacity having interlocking strips which extend from alternate sides of the inner wall of a hollow wave guide and which carries metallic cylinders as hole cylinders for the beam of the tube extending symmetrically in the longitudinal direction about the axis of the travelling-wave tube and forming the through openings for the beam, and wherein an intermediate electrode is disposed in the center of the space between two successive strips.

2. Description of the Prior Art Very often, in delay lines having a wide pass band,

only a small portion of the available band width is uti-' lized for amplification. In such a case, the line inputs and outputs and the vacuum window or windows are, as a rule, well matched only in the relatively narrow operating range. Therefore, in the event the matching of the attenuation elements in the portions of the pass band which are not utilized as operating range is not very good, particularly when there is a high amplification, there is a danger that parasitic oscillations are excited at the operating voltage of the tubes in these areas of the dispersion curves where the transitions and windows are badly matched.

Parasitic oscillations can be avoided if the pass band of the line is narrower, as a result of a diminished cell coupling, and the dispersion curve becomes steeper. For the operating voltages of the operating range, interference and noise in the adjacent dispersion curve sections of the pass band cannot excite the apparatus. These lines also have the advantage that the group velocity in the operating range changes very little. In order to reduce the pass band, it is an old and conventional expedient in the art to shorten the coupling slot whereby, however, the diameter of the delay line must be increased in order to obtain the operating range. However, in many cases, such an enlargement of the delay line diameter, particularly in tubes with periodic magnetic focusing, is disadvantageous or even impossible, since difficulties arise with the layout of the magnetic system. In addition to these difficulties, in such delay lines having larger diameters, the electrical longitudinal field strength increases with frequency, since at the upper limiting frequency less energy is stored in the coupling slot than at the lower limiting frequency. However, the high field strength in the proximity of the upper limiting frequency greatly increases the danger of pre-oscillation of the tubes when the operating current and the line voltage are simultaneously switched into the circuits.

It is therefore highly desirable and a primary object of the present invention to provide a delay line for travelling-wave amplification tubes wherein a steeper course of the dispersion curve can be achieved without enlarging the diameter of the delay line.

SUMMARY OF THE INVENTION According to the invention, a delay line is provided in a hollow wave guide having spaced-apart metallic beam cylinders extending symmetrically in the longitudinal direction about the axis of the travelling-wave tube and wherein intermediate electrodes are provided as diaphragms which extend from the inner wall of the hollow wave guide, the intermediate electrodes having apertures whose inner edges are at a distance from the delay line axis such that these edges are considerably farther from the delay line axis than the outer radius of the spaced-apart beam hole cylinders. The apertured diaphragms extend in the peripheral direction at least over the largest portion, as viewed in the axial direction of the hollow wave guide, of segment-shaped coupling openings laid bare by the beam hole cylinders and their connecting apparatus. The diaphragms may consist of segment-shaped cut-out pieces of a metal ring, whereby the angular apertures of the segments correspond substantially to the angular apertures of a coupling aperture.

A particularly simple arrangement is obtained in a further development of the invention in that the intermediate electrodes represent metal rings which bear against the inner wall of the hollow wave guide and whose central inner apertures have a diameter which is substantially larger than the outer diameter of the beam hole cylinders.

Travelling-wave tubes of the type initially described having intermediate electrodes are old in the art, for example see U.S. Pat. No. 3,181,024, whereby the intermediate electrode does not extend from the inner wall of the hollow wave guide and whereby the diameter of the inner aperture is substantially the same as the diameter of the aperture of the beam hole cylinders. In the prior arrangement, variation of the slot factor is essentially achieved by the intermediate electrode, whereas the mode of operation of the steps set forth in the present invention lies in the displacement effect produced by the intermediate electrodes of the present invention.

By inserting the diaphragm in accordance with the invention, the magnetic coupling of the cells in the proximity of the limiting frequency is diminished, whereby, although a small additional capacitive load is generated, the influence of the reduced magnetic coupling is clearly evident. The insertion of the diaphragms in accordance with the invention effects a movement of the lower limiting frequency toward shorter waves.

By way of contrast, the diaphragms in accordance with the invention diminishes the magnetic degenerative coupling in proximity of the upper limiting frequency and produces a strong capacity load. Both of these effects move the upper limiting frequency in the same direction towards longer waves. The dispersion curve turns, therefore, as a result of the contrary movements of the two limiting frequencies under the influence of the intermediate electrodes, substantially about the central wave length of the pass band and becomes steeper.

By varying the length of the hole cylinder for the beam, the capacitive load at both ends of the pass band is influenced in the same direction. Hence, a variation of the length of the hole cylinder for the beam effects only a parallel movement of the dispersion curve.

' Therefore, with a fixed coupling aperture, the desired In a delay line as provided by the present invention, which has intermediate electrodes, the coupling resistance diminishes more rapidly with increasing frequency than in a delay line having a short double slot without such intermediate electrodes. However, the delay line in accordance with the present invention has, in addition to the very substantial advantage of a smaller delay line diameter, the additional advantage of a smaller longitudinal field strength in the proximity of the upper limiting frequency, so that the danger of excitation for parasitic oscillation is reduced when the circuit is switched in.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the invention, will be readily apparent from the following description of the preferred embodiment thereof, taken in conjunction with the accompanying drawing, although variations and modifications may be effective without departing from the spirit and scope of the novel concepts of the disclosure, and in which:

FIG. 1 illustrates a typical trace of a dispersion curve for delay lines of the prior art;

FIG. 2 illustrates a desired steeper trace of a dispersion curve for a delay line in accordance with the invention;

FIG. 3 is a fragmentary sectional view taken through the longitudinal axis of a delay line arrangement in accordance with the invention wherein the intermediate electrodes are constructed as metal rings; and

FIG. 4 is an end view of the delay line illustrated in FIG. 3 as viewed along the direction of its longitudinal axis.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, the degree of delay c/v is plotted over the wave length A, whereby the zone between points A and B correspond to the desired operating range. As can be seen from the drawing, in a delay line having a dispersion characteristic as illustrated in FIG. 1, there is the danger that at the operating voltage of the operating range parasitic operations could be effected in the zone B-C of the pass band. There is no such danger with a delay line having a dispersion characteristic as illustrated in FIG. 2, which is the object of the steps taken in accordance with the present invention.

In the exemplary embodiment of a delay line in accordance with the invention illustrated diagramatically in FIGS. 3 and 4, arcuate-shaped members 2 extend from the inner wall of a hollow wave guide 1, alternate arcuate-shaped members extending from opposite sides of the wave guide, which members 2 each carry a beam hole cylinder 3 at their inner or distal ends.

In the zone between two successive arcuate-shaped members 2 there is provided an intermediate electrode in the form of a metal ring 4. The metal ring 4 includes an aperture 4 having a diameter which is larger than the outer diameter of the beam hole cylinders 3. It

should be noted at this point, as previously mentioned,

it is extremely important that the diameter of the aperture 4 be greater than the outer diameter of the beam hole cylinder 3 in that with approximately equal diameters of the aperture 4' and the openings 5 for the beam, the intermediate electrode would not operate in the direction of the displacement effect of the line currents, but with simultaneous constriction of the openings 5, a stronger influence on the slot factors is obtained. By varying the diameter of the inner conductor of the ring 4 and of the length h of the hole cylinders 3 for the beam, the desired characteristic of the dispersion curve illustrated in FIG. 2 can be adjusted.

We claim:

1. In a delay line for travelling-wave amplification tubes with a negative dispersion for the fundamental space mode of the type having a hollow wave guide having an inner surface, a plurality of hollow cylindrical elements spaced-apart longitudinally of the wave guide and individually connected to the inner surface of the wave guide to form openings for the beam of the tube, and intermediate electrodes disposed between adjacent ones of said hollow cylindrical elements, and having a dispersion characteristic defined between lower and upper limiting frequencies, the improvement therein comprising:

means for changing the dispersion characteristic including the provision of each of said intermediate electrodes as a ring,

each said ring including means defining an aperture having an edge concentric with the longitudinal axis of the delay line and a diameter which is greater than the diameter of the hollow cylindrical elements, whereby the lower limiting frequency is shifted toward shorter waves and the upper limiting frequency is shifted toward longer waves.

2. A delay line for a travelling-wave tube with a negative dispersion for the fundamental space mode, comprising: a hollow wave guide having a longitudinal axis and an inner wall, a plurality of arcuate-shaped members spaced-apart along the longitudinal axis and extending from the inner wall alternately on diametrically opposite sides of said wave guide, a plurality of hollow cylindrical elements individually carried concentric of the longitudinal axis by individual arcuate-shaped members, and a plurality of metal rings individually disposed between adjacent hollow cylindrical elements and each having an outer edge secured to said inner wall and an inner diameter greater than the outer diameter of said hollow cylindrical elements to capacitively load the line greater for higher frequencies of its operating range than for lower frequencies of the range to define a steep dispersion characteristic to prevent parasitic oscillations upon energization.

3. A delay line as set forth in claim 2, wherein each of said metal rings includes a solid body portion extending from said inner wall of said hollow wave guide to said inner diameter of the respective ring. 

1. In a delay line for travelling-wave amplification tubes with a negative dispersion for the fundamental space mode of the type having a hollow wave guide having an inner surface, a plurality of hollow cylindrical elements spaced-apart longitudinally of the wave guide and individually connected to the inner surface of the wave guide to form openings for the beam of the tube, and intermediate electrodes disposed between adjacent ones of said hollow cylindrical elements, and having a dispersion characteristic defined between lower and upper limiting frequencies, the improvement therein comprising: means for changing the dispersion characteristic including the provision of each of said intermediate electrodes as a ring, each said ring including means defining an aperture having an edge concentric with the longitudinal axis of the delay line and a diameter which is greater than the diameter of the hollow cylindrical elements, whereby the lower limiting frequency is shifted toward shorter waves and the upper limiting frequency is shifted toward longer waves.
 2. A delay line for a travelling-wave tube with a negative dispersion for the fundamental space mode, comprising: a hollow wave guide having a longitudinal axis and an inner wall, a plurality of arcuate-shaped members spaced-apart along the longitudinal axis and extending from the inner wall alternately on diametrically opposite sides of said wave guide, a plurality of hollow cylindrical elements individually carried concentric of the longitudinal axis by individual arcuate-shaped members, and a plurality of metal rings individually disposed between adjacent hollow cylindrical elements and each having an outer edge secured to said inner wall and an inner diameter greater than the outer diameter of said hollow cylindrical elements to capacitively load the line greater for higher frequencies of its operating range than for lower frequencies of the range to define a steep dispersion characteristic to prevent parasitic oscillations upon energization.
 3. A delay line as set forth in claim 2, wherein each of said metal rings includes a solid body portion extending from said inner wall of said hollow wave guide to said inner diameter of the respective ring. 